Reading
A short shelf, kept short on purpose.
Worth owning
Any decent limnology textbook will do more for you than a stack of field guides, because the field guides tell you what a thing is called and the textbook tells you why it is there. I would rather know why.
Worth borrowing
The older county natural-history surveys are wonderful and almost entirely out of date, which is itself the interesting part: the baseline they describe is not the one you will go and stand in.
Not worth it
Anything that opens by telling you water is life. I know. That is why I am reading the book.